(CNN) -- Sen. Barack Obama will hold a rally in the Illinois capital of Springfield on Saturday, his campaign announced Tuesday, increasing speculation that his choice for vice president could be announced in the same town where the Democrat launched his own bid for the White House.

The rally will occur just days before the start of the Democratic National Convention in Denver, Colorado, which begins August 25. It will kick off a tour of battleground states leading up to the Democratic convention, Obama's campaign announced.

It is widely expected that Obama will name is selection for vice president this week, possibly as soon as Wednesday.

The Springfield rally will come after Obama completes a 2½-day bus tour across North Carolina and Virginia, when he will emphasize his economic platform.

Obamaofficially announced his own presidential candidacy on the steps of the Old State Capitol in Springfield in February 2007. The Old State Capitol is where Illinois's most famous politician, President Lincoln, served in the state legislature.

The announcement of weekend rally came the same day Obama's Republican rival, Sen. John McCain of Arizona, berated him for not supporting more offshore oil drilling, arguing that more drilling is necessary if America is to achieve energy independence.

McCain traveled to a Chevron oil rig dubbed the Genesis near New Orleans, Louisiana, in the Gulf of Mexico to deliver his attack on Sen. Barack Obama.The presumptive Republican presidential nominee's earlier trip to a rig was canceled because of weather.

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"Sen. Obama opposes new drilling," McCain said. "He has said it will not 'solve our problem' and that 'it's not real.' He's wrong, and the American people know it," McCain said.

Obama said this month he would reconsider his opposition to additional offshore drilling if more drilling was part of an overall plan to lower energy costs.

McCain argues that the law banning additional offshore drilling must be lifted to help find a solution to high energy prices.

"New drilling has to be part of our energy solution. It will not solve this problem alone. Alternative energy will not solve this problem alone. Conservation will not solve this problem alone. Solving our energy crisis requires an 'all of the above' approach," McCain said.

"It will require aggressive development of alternative energies like wind, solar, tidal and biofuels. It also requires expanding traditional sources of energy like clean coal, nuclear power and offshore drilling like that done on this rig."

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In his remarks to a veterans group Tuesday, Obama disputed McCain's charge that he changed his positions on Iraq for political expediency, saying "the times are too serious for this kind of politics."

McCain "is a man who has served this nation honorably, and he correctly stated that one of the chief criteria for the American people in this election is going to be who can exercise the best judgment as commander in chief," Obama said Tuesday at the Veterans of Foreign Wars convention in Orlando, Florida.

"But instead of just offering policy answers, he turned to a typical laundry list of political attacks."

Addressing the same group the day before, McCain said Obama's opposition to President Bush's "surge" strategy, which increased troop levels in Iraq in 2007, and his response to the crisis in Georgia raised questions about his judgment. Watch as Obama says Russia must abide by a cease-fire »

"Behind all of these claims and positions by Sen. Obama lies the ambition to be president. What's less apparent is the judgment to be commander in chief," McCain said.

Obama said Tuesday that he would never question McCain's love for his country and that it was unfair of the Republican to question his.

"When I look out at this audience, I see people of different political views. You are Democrats and Republicans and independents. But you all served together and fought together and bled together under the same proud flag. You did not serve a red America or a blue America; you served the United States of America."